One year ago, I posted an article about making the most of social distancing as the world started locking down due to the rapid spread of Covid-19. Here in March 2021, the news is looking much better: vaccines are being distributed at a record pace across the globe and number of cases and deaths are mostly on the decline.
As I look back at the Social DX Bucket List I made last year, I’m happy to see that I actually accomplished about 64% of the goals I listed. I knew some of those goals would take well over a year to achieve (the QRP EME one especially).
In particular, I’m chuffed that I braved up and started doing Parks On the Air (POTA) and Summits On The Air (SOTA) activations in CW (Morse Code). That was a huge step for me and I’ll freely admit: I was nervous about it. But in July 2020, I managed to do my first CW activation and since then it has become my choice mode of operating in the field. CW is such a simple mode and so efficient–plus it gives me a sense of connection with the roots of radio communications.
I also accomplished a few things I never set out to do:
Both of my 13 year old daughters studied for and passed their Technician class exams. One just passed her General as well.
Not a typical radio year for me
In a “normal” year, I do way more SWLing than I do ham radio activity.
Last year, I started doing caregiving for my parents in my hometown–I’m typically there 2-3 days a week. While I’ve done shortwave listening and even a little MW DXing in my hometown, I typically don’t have a lot of time, especially in the evening hours. I just want to hit the sack early. QRM is also debilitating there and while I’d like to install a permanent Loop On Ground antenna to mitigate the noise (you heard that right, Andrea!) I’m not entirely sure I’d even have the dedicated listening time to justify it. When I’m there, I like to spend quality time with my folks.
In general, I’ve had much less free time. Indeed, if you’ve written to me via email, you’ll know this based on how long it’s taken me to reply. It can take several weeks especially if the reply requires a detailed response (which many do).
En route to, and on the way back from my hometown, I’ve found that doing park and summit activations has been very rewarding. Last year, I believe I completed a total of 82 park activations.
POTA has given me an excuse to explore public lands I’ve never visited before. Plus, I love nothing more than taking radios to the field–both receivers and transceivers.
Hamming and SWLing
At the end of the day, I’m an SWL and a ham radio operator. I find the two activities complimentary.
Side note: As I mentioned in my Winter SWL Fest presentation this year, it saddens me when I receive angry emails from readers after I post items that are ham radio related. We’ve upwards of 7,000-10,000 daily readers on the SWLing Post and the number of complaints are a teeny, tiny fraction of our readership. I only receive messages like this about once a month and they typically say something akin to “I don’t like the ham radio stuff, so if you don’t stop posting it, I’m leaving!” (FYI: That’s a real quote taken from the last one I received in January). I can only assume that at some point in the past, a ham radio operator has been a jerk to this and other radio enthusiasts. It’s a shame, too. I hate seeing the negative impact of one loud troll compared with the encouragement and support of much better people. All of my ham radio friends are not only supportive of SWLing, but almost all got their start in radio via the shortwaves. I’m certainly a case in point.
I love all things radio and I believe the SWLing Post is a reflection of that. If it offends you, then it might make sense to surf somewhere else.
Now where was I? Oh yeah…
POTA and SOTA outings have helped to satisfy some of my travel cravings as well. I miss going to radio conventions, hamfests, and especially traveling internationally with my family. We are a family who love national parks, forests, and other wildlife areas. Having an excuse to explore public lands we haven’t visited before has been amazing fun.
After POTA activations, I’ll often do a little SWLing since I already have an external antenna up and it’s typically connected to a good general coverage transceiver in a spot with zero RFI or QRM. I’ve especially enjoyed my DXing sessions with the superb Icom IC-705.
One indicator that I did less radio listening last year was the low number of recordings I made. I checked my audio folder recently and saw that I only made a couple dozen recordings–most were staple broadcasters, not rare or special DX.
At the end of the day, I realize that when I do SWLing sessions I like to have dedicated time–at least an hour or two–with headphones on, losing myself on the radio dial. I simply haven’t had many opportunities this past year to make that a reality.
That’s okay, though. The great thing about the shortwaves is that they’re always there, patiently waiting for us to dive back in!
I’m really not sure what’s in store for me this year, but I know it’ll involve a lot of radio time and that pleases me to no end. I’ve made a few fun goals, but my hope is that, by the end of the year, I may even be able to do some proper travel–maybe even take a flight!
I do know this: I have an even more profound appreciation for my radio enthusiasm as I realize it’s the perfect space to travel and explore the world no matter how “locked down” things are. Based on feedback from readers and contributors to this site, I know I’m not the only one who feels this way.
How about you?
Did your radio activity change or pivot this past year? Did you have more or less time to hit the airwaves? Please comment!
PC keyer and AM modulator: A 15-components versatile keyer and powerful PSU modulator for the EMTX (Emergency Transmitter)
by Kostas (SV3ORA)
Schematic of the keyer and modulator (on the left) for the EMTX. The EMTX schematic is shown as well on the right, to determine the connections to the keyer/modulator.
My very successful emergency transmitter (EMTX) was only capable of CW or other slow speed ON/OFF keying modes. Then I thought, why not “give voice” to the design? CW is good, but it is half of the fun. If you could use your simple CW transmitter to send out your voice as well, this would be great. You could now chat comfortably on the nets or use any digital radio amateur mode and have much more fun. The simplest modulation you can apply to an existing CW transmitter, is the AM modulation. And whereas this is an old modulation, mostly abandoned by HAMs due to beeing inefficient, there are still AM nets on HF. But do not forget, AM can also be heard by SSB receivers by zero-beating the receiver to the AM carrier. So you could still use your simple AM transmitter to QSO with the SSB guys!
Along with the modulator, there is also a versatile keyer embedded to the circuit, so that the EMTX can be manually keyed with different ways or automatically keyed by audio tones from the PC. For more information on the keyer, keep reading.
The AM modulator
In the old days, the most common way to apply AM modulation was to modulate the high voltage to the plate of the tubes, using a transformer and a powerful audio amplifier. In low voltage solid state circuits, you can still do it using transformers, but you can also use series transistors instead of the transformer. All these things require many components and/or powerful AF amplifiers if one is to modulate higher power transmitters. This does not match the keep-it-simple design I am trying to achieve here.
So I thought of a simple trick with the use of the extremely common LM317 regulator, used as a modulated power supply. This modulator uses just a few common cheap components and it is able to achieve remarkably good modulation levels for it’s parts-count, just from line audio input. It juices every bit of the internal circuicity of the LM317, just look at where the base current of the 2N2222 comes from.
The AM modulator is a kind of novelty. Whereas there is nothing special in a modulated power supply, this circuit has some interesting properties. It is amazingly sensitive and it is able to provide lots of modulated current to any low power transmitter that it can feed. It can be easily driven by the line output of any laptop (around 20% volume) and provide a very good depth modulation to the transmitter. Charles Wenzel was kind enough to do a simulation on the circuit I developed, which is shown below.
His simulated circuit is a slight variation (for measurement purposes). The resistor to ground on the base stabilizes the bias and the ratio of R1 and R2 set the output voltage (0.6 volts across R2 gives about 8 volts across R1). He put in an emitter resistor just for good measure. Same for the series resistor from the source. Charles words, “I don’t know how believable these results are but it looks pretty darned good!”.
The circuit is being used as a current booster, the current being the supply to the transmitter and dependent on the voltage it produces. The LM317 always tries to keep 1.25V between it’s output pin and “adj” pin but where we benefit here is the current at the “adj” pin is very low, so it is easier to apply audio to it. Effectively, the error amplifier inside the voltage regulator is used as an additional amplifier stage. The output pin voltage varies according to the voltage on the “adj” pin so if we use it to bias the transistor we get negative feedback which improves the quality of the modulation. More output voltage = more bias current = lower output voltage. The result, is a very cheap, low components-count, very sensitive AM modulator that can supply lots of power to easily drive the transmitter and produce a clean and deep AM modulation!
The AM modulator bias is set with the 1M potentiometer. Depended on the bias level, the idle carrier on the EMTX can be set from about 0.5W all the way up to 8W. Needless to say that this modulator can modulate any similar power transmitter, not just the EMTX.
If it is to modulate the EMTX from the PC, so as to use the different digital modes, there must be a way to key it also from the PC. This is why I decided to embed into the same circuit, a PC keyer which is triggered by the line audio of the PC, but also triggered manually (internal or external key). Keying by audio tones was decided, because modern PCs do not have LPT ports to trigger directly by DC. This keyer uses a reed relay to reliably, fastly and scilently key the EMTX, which is activated by a transistor. The base current for the transistor is derived from the audio signal after rectification. The incoming audio from the PC line passes through the mini audio transformer to increase its voltage, it is rectified and then charges the shunt capacitor to drive the base of the transistor. The keyer “speed” (decay) is determined by the shunt capacitor size. The circuit starts to trigger from about 50-60% of my sound card output signal level.
The relay used to key the EMTX, must be able to tolerate at least 1A of switching and carrying current. Note that the relay contacts switching current is not the same as the contacts carrying current. Reed relays are the best especially if you want long relay life, noiseless operation and very fast switching speeds, like the ones used in Hellshreiber. If you can’t find such a relay, you can use a reed switch capable of 1A of switching and carrying current and then place a suitable electromagnet close to it, so you can build the relay yourself. If you do so, find the best point where the reed switch responds to the electromagnet.
The keyer relay must be as close as possible to the emitter of the transistor used in the EMTX. The connectors at the back of the EMTX and the keyer/modulator have been physically placed so that when the two units are side by side, a very short link cable is required for this purpose. With the two devices placed close together, you can now use any length of cable for your manual external key, which is now connected to the “EXT” connector of the keyer/modulator.
The keyer does also have an internal mini straight key. I find this idea very nice, to avoid extra cables. It is not the most convenient key in the world, but it is there along with the transmitter every time you need it. By using a special panel switch from apem, I was able to triple this switch usage for the different modes of the keyer. The vinyl lever cap you see in the next picture, is the original part of the switch, to make it easier to key with your finger. But you may build such a part on your own, to fit on other switches types.
The switch is an ON-OFF-(ON momentary) switch type. In the default (middle) position, only the PC keying action is activated. In the top position (ON), the keyer is always active, which is useful for broadcasting audio (into a dummy load). The bottom (ON momentary) position, is the manual PTT action. This is used as a straight key on OOK operation, or as a PTT on AM voice operation. Simple and effective!
Initially, I used one channel of the PC sound card for triggering the keyer and also as an AF signal for the AM modulator, but this caused several problems of unreliable keying or distortion. So I decided to use a second separate AF input (KAF) to key the keyer. This second input, uses the other channel of the stereo sound card. With the addition of this input, there is no interaction between the keyer and the modulator. The AF levels that the keyer and the modulator require, can be set independently. Instead of adding more hardware for the purpose, I have chosen to set these levels by adjusting the volume and the balance of the sound card, which works great. Also, programs like Fldigi, have options for using one of the two channels of the stereo sound card as a keying interface (PTT channel), which makes the keying efen more reliable. When the program is in transmit mode, a continuous tone is heard on the PTT channel. This steady tone, is used by the keyer as a reliable keying signal, independent of the audio signal of the digital mode that modulates the modulator. This solution works very reliably for any mode. But if the program you are using does not have an option for a PTT channel, that is ok, as the keyer works reliably even without this feature. For voice communication or broadcasting music (into a dummy load) you just use the internal key switch as a PTT to handle these modes.
Prior to building the keyer and the modulator in the same device, I had tested the circuits independently quite a few times, to ensure the results can be reproduced. The modulation quality and depth out of the AM modulator have to be listenned to be believed. I have not made any linearity measurements, I just trust my ears on this one. It works great on music as well as on voice. Apart from that, this is the most sensitive AM modulator I have ever built, requiring only a small fraction of the line level output of the PC sound card.
When modulated by this modulator, the EMTX shows no audible signs of FM modulation. I switched my receiver to SSB and I could perfectly zero beat the AM modulated music signal which stayed on frequency and it’s tone did not change during loud audio signal music. Switching back and forth from SSB to AM modulation on the receiver, I did not notice any difference in the audio quality, apart of course from the narrower bandwidth on SSB modulation, due to the narrower IF filter inside the receiver on SSB.
The AM/OOK switch is used to select the modulation applied to the EMTX. When the keyer is set to be triggered by audio from the PC, at the OOK position, the EMTX is just switched on and off by the audio tones applied to the keyer, or by the manual key, internal or external (connected to the “EXT” connector). At AM position, the EMTX is switched on by the audio signal applied to the KAF connector and at the same time AM modulated by whatever audio signal is applied to the AF connector. On voice communications, the momentary position of the internal key is used as a PTT. On music broadcasting (into a dummy load) the non-momentary position of the internal key is used to keep the keyer always active.
Back connections to the EMTX.
Pictures of the finished keyer/modulator. You don’t have to build it that nice-looking if you don’t care.
Modulator prototype and EMTX built on a breadboard. Yes it worked just fine onto a piece of wood.
Thank you so much for sharing this brilliant and simple project with us, Kostas. Your handiwork is absolutely brilliant too!
Many thanks to SWLing Post contributor, Kostas (SV3ORA), for sharing the following guest post which originally appeared on his radio website:
Emergency transmitter: An 8-component, high-power 40m/30m transmitter to get you quickly on the air
by Kostas (SV3ORA)
QRP is all about doing more with less. This is more than true, with the construction of this cheap, simplistic transmitter presented here. It is designed primarily as an emergency transmitter (EMTX) that can be built or serviced in the field or at any home. However, it can be used as a HAM radio transmitter as well. Do not judge by its low components count though. This transmitter is powerful, more powerful than anything the QRPers would dream of. It is just remarkable how 8 components can lead in so much output power, that lets you communicate with a big part of the world, when propagation conditions are right. It is very difficult for a circuit to match that kind of simplicity in balance with such performance.
Following my detailed instructions, the EMTX can be reproduced easily, within hours. The result is always success, this is one of the circuits that are not critical at all and a successfully working transmitter can be reproduced every time. I have built this transmitter several times, using similar components (even toroids) and it always worked. The transmitter meets the next expectations:
1. Output power (including harmonics): A few mW up to 15W (depended on transistor, crystals and voltage/current used) at 50 ohm.
2. It can drive any antenna directly, 50 ohm or higher impedance, without external tuners.
3. Bands of operation: Currently 40m, 30m
4. Mode: CW, Feld-Hell (with external switching circuit), TAP code and any other ON/OFF keying mode. AM modulation has been easily applied too.
5. Options like reverse polarity protection diode (useful in the field when testing different unknown polarities PSUs) and current meter (for easier tuning) are available.
The purpose of this transmitter is to be used primarily as an emergency transmitter. This poses several challenges that influence the design of the transmitter:
1. It must be able to be built or serviced easily in the field or at any home, with components that could be salvaged from near by electronics sources or a small electronics junk box. This means that components count should be kept very low and they must not be rare to find but commonly available parts. As a side effect cost would also be kept small, if one is to buy any component. Also, the active components must be interchangable with many other devices without the need for the design or the rest of the circuit components to be changed.
2. It must be able to operate from a very wide range of DC voltage sources and at relatively low current, so that common house power supplies could be used to supply power to it. Such devices include linear or switched mode power supplies from laptop computers, routers, printers, cell phone chargers, Christmas lights or any other device one might have available.
3. It must be capable of transmitting a powerful signal, so that communication is ensured. An emergency transmitter that is capable of a few mW of output power, might be heard locally (still useful, but there are handheld devices for that already) but isn’t going to be of much usage if it can’t be heard really far away.
4. It must be capable of loading any antenna without external equipment required. In an emergency situation, you just don’t have the luxury of building nice antennas or carrying coaxial cables and tuners. There may be even extreme cases where you can’t even carry a wire antenna and you depend on salvaging wire from sources in the field to put out a quick and dirty random wire antenna.
5. Adjustments of the transmitter should be kept minimum without the help of any external equipment and there must be indication of the correct operation of the transmitter or the antenna in the field.
This transmitter has been designed so that it can operate with any NPN BJT in place. This includes small signal RF and audio transistors and high power RF transistors like the ones used on HF amplifiers and CB radios. Despite 2sc2078 is shown in the schematic, just try any NPN BJT in place and adjust the variable capacitor accordingly. When you are in the field, you do not have the luxury of finding special types of transistors. The transmitter must operate with any transistor in hand, or salvaged from near-by equipment. Of course the power capability of the transistor (as well as the crystal current handling) will determine the maximum VCC and current that can be applied to it and hence the maximum output power of the transmitter. Some of the most powerful transistors I have used, come out of old CB radios, such as the 2sc2078, 2sc2166, 2sc1971, 2sc3133, 2sc1969 and 2sc2312. There are many others. As an example, the 2sc2078 with a 20v laptop PSU, gave 10-12W of maximum output power into a 50 ohms load.
Schematic of the 8 components EMTX for the 40m/30m bands. Components with gray color are optional.
This is the most uncommon part of the transmitter. You have to find the crystal for the frequency that you want to operate on. Crystals within the 40m or 30m CW segments are not that common. Further more if you operate the transmitter at high powers and currents, you will notice crystal heating and chirp on the frequency of the transmitter. The current handling capability of your crystal die inside the crystal case, will determine the chirp and the amount of crystal heating. You can still work stations with a chirpy transmitter provided that the chirp is not that high, so that it can pass through the CW filters of the receivers. However, if a small chirp annoys you or if this chirp is too much, then you have to use these vintage bigger size crystals (e.g. FT-243), that can handle more current through them. But these are even more uncommon today.
The approach I have used in my prototype, was to connect more than one HC-49U crystals of the same frequency in parallel, so that the current is shared among them. This reduced the chirp at almost unnoticeable levels, even at high output power, just if I was using a single FT-243 crystal, or even better in some cases. Again, this is optional, but if you want to minimize chirp (and crystal heating) without searching for rare vintage crystals, this is the way to go.
A bit of warning. If you notice a very high chirp when plugging in a crystal to the EMTX, you should consider this crystal as inappropriate for this transmitter, as it cannot handle the current required. If you continue to use this inappropriate crystal, you could easily crack it inside and set it useless. Don’t use these tiny HC-49S crystals, they won’t work.
The current meter:
A 1Amp (or even larger) current meter can be used to monitor the current drawn by the transmitter during key down. The recommended current operating point is anywhere between 450mA to 1A, depended on the output power (and harmonics) level you want to achieve. The current point is set by the variable capacitor. I would avoid setting the current to more than 1Amp, although it can be done. The use of the current meter is optional, but along with the incandescent bulb, will give you a nice indication of the correct tuning of the transmitter, so that you do not need to have an external RF power meter connected to the transmitter output. If you do have, then you can remove the current meter. If you don’t have a 1Amp analogue meter available, but a smaller one, you can parallel a low value power resistor across the meter. In my case, I only had a 100uA meter and I paralleled a 0.15 ohms 5W resistor across it to scale down 1Amp to 100uA, The resistor value depends on the internal meter resistance so you have to calculate this for your specific meter. When the 2sc2078 is used at 20V, 500mA in the current meter indicates around 5W of output power, 600mA indicates around 6W, 700mA 7W, 800mA 8W, 900mA 9W and 1A around 10W. So the current meter can be used as sort of power meter without the need to do any scaling on it.
The incandescent bulb:
A current meter alone, without the use of the incandescent bulb, will not give you the right indication of the operation of the transmitter. In some cases, the transmitter might be drawing current without actually generating much, or even any RF. When you are in the field you do not want to carry extra monitoring equipment with you. The incandescent bulb will light on when the transmitter oscillates. It monitors the actual RF signal, so it’s brightness changes according to the amount of RF power the transmitter produces. Along with the current meter reading, this is just what you need to know in order to set the variable capacitor properly. Note that the bulb will not lit at very low signal levels. The one used in the prototype starts to glow up from a bit less than 1W. Miniature incandescent bulbs may not be that easy to find nowadays. However, there is a good source of these, that almost anyone has in their houses. This source is the old Christmas lights. You do save old Christmas lights, don’t you? The incandescent bulb indicator as well as it’s single turn winding on the transformer, are optional components. If you have an RF power meter connected to the transmitter, you can remove these.
The protection diode is an optional component to the circuit. If you are in the field, correct polarity of a power supply may not be obvious. Without a multimeter it might me difficult to determine the correct polarity of the PSU. A power diode (I used a 6A one) will protect the transistor from blowing up in the event that reverse polarity is connected to the circuit.
The Cx and Cy:
The Cx and especially the Cy capacitors need to be of good quality. The Cy will get hot on high output power if it isn’t. In the tests, I have used homemade gimmick capacitor and even double-sided PCB as a capacitor for Cy and they all got hot at high power. Silver mica capacitors run much cooler and they do make a small difference in the output power, so I suggest to this type. Cy must be able to handle quite a lot of voltage, so silver mica type is ideal.
The variable capacitor:
The variable capacitor can be air variable or ceramic, although I prefer air variables in tis application. In any case it must be able to handle a high voltage just as the Cy.
The key directly shorts the transistor emitter to the ground, therefore it is a part of the active circuit. For this reason, I suggest the key leads to be kept as short as possible. The key must be able to handle the voltage (20v) and current (up to 1A) on its contacts, which is usually not a big deal.
The construction of the transformer is shown below step by step. Note that if you decide that you don’t need to drive higher impedance loads but just 50 ohm ones (eg. antenna tuners or 50 ohm matched antennas), you just need to wind 2t in the secondary and not 14t. You also don’t need any taps of course.
Take a piece of 32mm external diameter PVC pipe from a plumber’s shop. Alternatively, a suitable diameter pills box can be used, or any other suitable diameter plastic tube.
Cut a 4cm piece out of this tube. 4cm is the minimum length required.
Below a 4cm PVC tube has been cut in size.
Wind 16 turns of 1mm diameter enameled wire onto the PVC pipe and secure the winding in place as shown in the picture below. Notice the winding direction of the wire. This is the primary of the transformer, the one that is connected to the two capacitors. Notice that this winding is wound a bit offset to the right of the pipe.
Wrap the winding with 3 turns of PTFE tape. It can be bought at any plumber’s shop, just like the PVC pipe. The PTFE tape will help in keeping the second layer turns in place and it will provide extra insulation.
Wind 2 turns of 1mm diameter enameled wire on top of the primary winding and secure the winding in place as shown in the picture below. Notice the winding direction of the wire, as well as it’s position relative to the primary winding. This is the feedback of the transformer, the one that is connected to the collector of the transistor.
Wind 14 turns of 1mm diameter enameled wire on top of the primary winding, starting from just next to the 2 turns one and secure this winding in place as shown in the picture below. Notice the winding direction of the wire, as well as its position relative to the primary and the 2 turns windings. This is the secondary (output) of the transformer, the one that is connected to the antenna. At this point do not worry about the taps yet.
Notice in the picture below, the way the windings are secured in place onto the pipe. The wire ends are passed through the pipe using small holes and then bent towards the ends of the pipe and once more to the surface of the pipe, where the connections will be made.
Wind 1 turn of 1mm diameter enameled wire onto the pipe and secure the winding in place as shown in the picture below. Notice the winding position relative to the other windings. This 1 turn winding is placed about 1cm away from the other windings. This is the RF pick up winding, the one that is connected to the incandescent bulb.
Use a sharp cutter (knife) and carefully scrap the enamel of all the windings ends. Do not worry if you cannot scrap the enamel at the bottom side of the wire ends (that touches to the pipe). We just want enough copper exposed to make the connection.
Tin the scrapped wire ends, taking care not to overheat them much.
Now it’s time to make the taps on the secondary winding. Use a sharp cutter (knife) and very carefully scrap the enamel of the wire at the tap points (number of turns). Take much care not to scrap the enamel of the previous and the next turn from each tap point. Do not worry if you just scrap the enamel at the top of the wire (external area). We just want enough copper exposed to make the connection.
Make each tap, a bit offset from the near by taps, like shown in the pictures. This will avoid any short circuits (especially at the 4, 5 and 6 taps) and it will allow for easier connections, especially if alligator clips are used to connect to the taps.
Tin all the tap points, taking care not to overheat them.
This step is optional and it depends on how you decide to do the connections to the taps. You may solder wires directly to the tap points, but in my case I wanted to use alligator clips, so I did the next: I took a piece of a component lead and soldered it’s one end to each tap point. Then I bent the component lead to U-shape and cut it accordingly. This created nice and rigid tap points for the alligator clip.
This step is optional and it depends on how you decide to mount the transformer to your enclosure. In my case, I wanted to create three small legs for the mounting. I cut three pieces of aluminum straps and made holes at both their ends. I made three small holes onto the transformer pipe end and mounted the aluminum straps using screws. After mounting them, I shaped the straps to L-shape. Then I used three more screws to mount the transformer to the enclosure.
The completed transformer is shown in the pictures above and below. The 6 connection points at the bottom of the pipe, are the low voltage points, whereas the 2 points at the top of the pipe, are the high voltage points.
If you have built the transformer as described, the bottom connections are as follows (from left to right):
Wire end 1, connected to the incandescent bulb
Wire end 2, connected to the incandescent bulb
Wire end 3, connected to the current meter
Wire end 4, connected to the current meter
Wire end 5, connected to the GND (ground)
Wire end 6, connected to the transistor collector
The top connections are as follows (from left to right):
Wire end 1, connected to the 25pF variable capacitor and the Cy fixed.
Wire end 2, is the 14th secondary tap and it is left unconnected, or tapped to the appropriate impedance antenna.
Videos of the EMTX in operation
I have made two small videos of the EMTX in operation.
The first 13.5MB video (right click to download), shows the operation when the transmitter is set for a bit less than 10W of output power.
The second 3.5MB video (right click to download), shows the operation when the transmitter is set for about 5W of output power.
EMTX chirp analysis
Every self-exited power oscillator (and even many multi-stage designs) exhibits some amount of chirp. Chirp is mainly considered as the sudden change in frequency when the power oscillator is keyed down. Apart from chirp, there is also the longer term frequency stability that may be considered. The chirp in the EMTX is surprisingly low, if it is built properly. Hans Summers, G0UPL has performed a chirp analysis on my EMTX (PDF) and the EMTX built by VK3YE and presented on YouTube. Hans, performed the analysis from the video/audio recordings of both transmitters. I sent him two videos, one with the EMTX set for an output power of 10W and one where it is set for 5W. The chirp at worst case (10W) was about 30Hz and at 5W in the order of 10Hz or so. Being so small, the chirp is almost undetectable by the ear and it surely poses no problems when passing the tone through narrow CW filters. This is an amazing accomplishment from a transmitter so simple and so powerful.
EMTX harmonics measurement
Every unfiltered transmitter will excibit harmonics at it’s output. This means that the output waveform has some distortion in comparison to a pure sinewave. Many of the transmitters I have seen, present a very distorted output waveform and absolutely need a LPF if they are to be connected to an antenna. I can’t say that this is true for the EMTX, because surprizingly, it has low distordion, despite the high output power it can achieve. Although a LPF is always a good idea, it is not that much needed on the EMTX. However you have to use one to comply with the regulations.
The image above, shows the measurements on the output of the EMTX, when it is set closely to 10W at 50 ohms. The main carrier is exactly at 9.9W and all the harmonics are less than 50mW! Also, the harmonics, do not extend into the VHF region.
The image below, shows the measurements on the output of the EMTX, when it is set closely to 5W at 50 ohms. The main carrier is exactly at 5.17W and all the harmonics are less than 9.6mW! Again, the harmonics, do not extend into the VHF region.
These small harmonics levels aren’t going to be heard very far at all, compared to the powerful carrier. This means only one thing. A LPF, although a good practice, is not mandatory in this transmitter. But you should better use one so that you comply with the regulations.
Many HAMs use just a watt meter to measure the output of their homebrew transmitters. This is not the proper way of doing it, because the watt meter is a non-selective meter. It will measure both the fundamental carrier and the harmonics, without being able to distinguish them. So in an unfiltered transmitter, or in a transmitter with a simple (often non measured) LPF, this way will give a totally false reading of the output power of the transmitter at the set frequency.
The proper way of accurately measuring the output power of a transmitter and the harmonics levels, is a spectrum analyzer. The FFT available in many modern oscilloscopes, having a dynamic range of approximately 50-55dB, is adequate for this purpose as well. A 50 ohms dummy load must be connected at the transmitter output and then the high impedance probe of the scope, is connected to the output of the transmitter as well. This was the way that the above measurements have been performed.
Here are some test transmissions, to determine how far one can get with such a transmitter. I have to say that there is an antenna tuner between the EMTX and my inefficient short dipole (not cut for 40m and not even matched to the coaxial). However I could still cover a distance of more than 2500Km even on the 5W setting.
A screenshot of the transmitter signal, as received on a WebSDR 2500Km away and when the EMTX is set for an output power of 10W.
Below, is a picture and an audio recording of the transmitter signal, as received on the same WebSDR and when the EMTX is set for an output power of 5W.
Pictures of the finished transmitter. You don’t have to build it that nice-looking if you don’t care.
EMTX prototype built on a breadboard. Yes it worked just fine onto a piece of wood.
This is a phenomenal project, Kostas. Thank you so much for sharing it with us. I love the simplicity of this design–truly form following function. With a little patience, anyone could build this transmitter.
Andy’s article caused me (yes, I blame him) to wax nostalgic about the popular FT-817 transceiver. You see, I owned one of the first production models of the FT-817 in 2001 when I lived in the UK.
At the time, there was nothing like it on the market: a very portable and efficient HF, VHF, UHF, multi-mode general coverage QRP transceiver…all for $670 US.
In 2001? Yeah, Yaesu knocked it out of the ballpark!
In fact, they knocked it out of the ballpark so hard, the radio is still in production two decades later and in demand under the model FT-818.
I sold my FT-817 in 2008 to raise funds for the purchase of an Elecraft KX1, if memory serves. My reasoning? The one thing I disliked about my FT-817 was its tiny front-facing display. When combined with the embedded menus and lack of controls, it could get frustrating at home and in the field.
When I told Andy about my ‘817ND purchase, he asked if I’d like to help him test the FT-817 Buddy board versions. How could I refuse?
Andy sent me a prototype of his Version 2 Buddy board which arrived in late November. I had to source out a few bits (an Arduino board, Nokia display, and multi-conductor CAT cable). Andy kindly pre-populated all of the SMD components so I only needed to solder the Arduino board and configure/solder the cable. I did take a lot of care preparing and soldering the cable, making sure there was no unintentional short between the voltage and ground conductors.
Overall, I found the construction and programming pretty straight-forward. It helped that Andy did a remote session with me during the programming process (thanks, OM!). Andy is doing an amazing job with the documentation.
I do love how the board makes it easier to read the frequency and have direct access to important functions without digging through embedded menus. While there’s nothing stopping you from changing the program to suit you, Andy’s done a brilliant job with this since he’s an experienced FT-817 user.
The Nokia display is very well backlit, high contrast, and easy very to read.
“Resistance is futile”
I mentioned on Twitter that, with the backlight on, the FT-817 Buddy makes my ‘817ND look like it was recently assimilated by The Borg.
Don’t tell any Star Trek captains, but I’m good with that.
Andy has a rev3 board in the works and it sports something that will be a game-changer for me in the field: K1EL’s keyer chip!
For more information about the FT-817 Buddy, check out Andy’s website. At time of posting, it’s not available yet, but as Andy says, “it’s nearly there!”
Of course, we’ll keep you updated here as well. Many thanks to Andy for taking this project to the next level. No doubt a lot of FT-817 users will benefit from this brilliant project!
This morning, I’m catching up with email and posts as I’ve had less online time these past few days (not a bad thing). I’m also trying to sort out and organize some of the gear in my compact shack/office.
As I do this, I can’t help but think through some of the radio projects that await me in 2021–so I started making a list.
2021 Radio Goals
Portable DXing: I hope I’ll be able to travel again in the latter part of 2021 and take my portable SDR pack to capture spectrum recordings in the field. I really miss doing this.
Carefully go through my portable radio collection and “thin the herd.” I’ve no intention of letting go of everything, but I’ve a number of small, inexpensive portables I never touch and don’t plan to use for comparisons
Purchase a few more cables and a mic to complete my multitrack recording and receiver comparison setup. Massive thanks to my friend, Matt Blaze, who’s helped me through this process.
Finally replace that faulty keypad on the Drake SW8! (This might be the first thing I do in the new year.)
Antenna Farm improvements and upgrades:
It’s time for the remote tuner box to get a rennovation!
I plan to re-build my remote tuner box (that’s served me so well for a decade–see photo)
install all new connectors, components, and change the balun
add a remote antenna switching device
beef up lightening protection
and replace all of the coax feed lines.
I also plan to add a home brew 80 meter vertical and possibly a 20M delta loop oriented E/W
QRP EME: I still need to sort out a VHF amplifier, antenna, connectors and cables for my QRP EME station. I hope to have the pieces together by mid 2021.
Build my QCX+ and QCX Mini transceivers (really looking forward to that!)
In truth? I’ve more goals than this, but I’m trying to be somewhat realistic. The top priority is investing time in my antenna situation at home. All of the coax lines are aging and I know are no longer up to spec. I see cable and even connectors as long-term consumables and it’s definitely time to reinvest!
How about you? What are your radio goals for 2021?
Also been modding the FT-817ND with a Buddy Board prototype by Andy (G7UHN). Installing version 3 in a few weeks!
Please comment and let us know what you’re plotting and planning! Inquiring minds want to know!
Here’s wishing everyone a happy & healthy New Year!
Thank you for being a part of the SWLing Post community!
Yesterday [Saturday, November 14, 2020] my family decided to make an impromptu trip to one of our favorite spots on the Blue Ridge Parkway at Richland Balsam–the highest point on the BRP.
Of course, it was a good opportunity to fit in a Parks On The Air (POTA) activation, but I had also hoped to activate Richland Balsam for Summits On The Air (SOTA) simultaneously.
It being well beyond leaf-looking season, we had hoped the BRP would be relatively quiet, but we were wrong.
Trail heads were absolutely jam-packed and overflowing with visitors and hikers. We’ve noticed a sharp hiker uptick this year in western North Carolina due in no small part to the Covid-19 pandemic. People see hiking as a safe “social-distance” activity outdoors, but ironically, hiker density on our single-track trails is just through the roof. One spends the bulk of a hike negotiating others on the trail.
The trail head to Richland Balsam was no exception. Typically, this time of year, we’d be the only people parked at the trail head but yesterday it was nearly parked full.
Being natives of western North Carolina, we know numerous side-trails and old logging/service roads along the parkway, so we picked one of our favorites very close to Richland Balsam.
We hiked to the summit of a nearby ridge line and I set up my POTA station with the “assistance” of Hazel who always seems to know how to get entangled in my antenna wires.
“I’m a helper dog!”
Taking a break from using the Icom IC-705, I brought my recently reacquired KX1 field radio kit.
I carried a minimal amount of gear on this outing knowing that there would be hiking involved. Everything easily fit in my GoRuck Bullet Ruck backpack (including the large arborist throw line) with room to spare.
I took a bit of a risk on this activation: I put faith in the wire antenna lengths supplied with my new-to-me Elecraft KX1 travel kit. I did not cut these wires myself, rather, they are the lengths a previous owner cut, wound, and labeled for the kit.
With my previous KX1, I knew the ATU was pretty darn good at finding matches for 40, 30, and 20 meters on short lengths of wire, so I threw caution to the wind and didn’t pack an additional antenna option (although I could have hiked back to the car where I had the CHA MPAS Lite–but that would have cut too much time from the activation).
I didn’t use internal batteries in the KX1, rather, I opted for my Bioenno 6 aH LiFePo battery which could have easily powered the KX1 the entire day.
I deployed the antenna wire in a nearby (rather short) tree, laid the counterpoise on the ground, then tried tuning up on the 40 meter band.
The ATU was able to achieve a 2.7:1 match, but I don’t like pushing QRP radios above a 2:1 match if I don’t have to. I felt the radiator wire was pretty short (although I’ve yet to measure it), so clipping it would only make it less resonant on 40 meters.
Instead, I moved up to the 20 meter band where I easily obtained a 1:1 match.
I started calling CQ POTA and within a couple of minutes snagged two stations–then things went quiet.
Since I was a bit pressed for time, I moved to the 30 meter band where, once again, I got a 1:1 match.
I quickly logged one more station (trusty N3XLS!) then nothing for 10 minutes.
Those minutes felt like an eternity since I really wanted to make this a quick activation. I knew, too, that propagation was fickle; my buddy Mike told me the Bz numbers had gone below negative two only an hour before the activation. I felt like being stuck on the higher bands would not be to my advantage.
Still, I moved back up to 20 meters and try calling again.
Then some radio magic happened…
Somehow, a propagation path to the north west opened up and the first op to answer my call was VE6CCA in Alberta. That was surprising! Then I worked K3KYR in New York immediately after.
It was the next operator’s call that almost made me fall off my rock: NL7V in North Pole, Alaska.
In all of my years doing QRP field activations, I’ve never had the fortune of putting a station from Alaska in the logs. Alaska is a tough catch on the best of days here in North Carolina–it’s much easier for me to work stations further away in Europe than in AK.
Of all days, I would have never anticipated it happening during this particular activation as I was using the most simple, cheap antenna possible: two thin random lengths of (likely discarded) wire.
People ask why I love radio? “Exhibit A”, friends!
After working NL7V I had a nice bunch of POTA hunters call me. I logged them as quickly as I could.
I eventually moved back to 30 meters to see if I could collect a couple more stations and easily added five more. I made one final CQ POTA call and when there was no answer, I quickly sent QRT de K4SWL and turned off the radio.
I still can’t believe my three watts and a wire yielded a contact approximately 3,300 miles (5311 km) away as the crow flies.
This is what I love about field radio (and radio in general): although you do what you can to maximize the performance of your radio and your antenna, sometimes propagation gives you a boost when you least expect it. It’s this sense of wireless adventure and wonder that keeps me hooked!
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